In 343gs a marine states the Covenant tried hard to lock the Flood door but the thing is the Covenant were already running from the flood before the marines accessed the chamber. This would also explain the bodies outside the room. With hard enough viewing, I saw human blood next to the very place where the dead marines were which means the flood had already been let out before the marines arrived in the chamber. The covenant must have securely locked the Flood door before but then maybe an accident (presumably stupid grunts) opened it and a small portion of flood was let out before the covenant locked the door again without them noticing. This would explain a few scenes, firstly the [sic] Flood Elite [at the log]. I also noticed the Flood Elite was a yellow blip on the motion tracker but a red target on the reticule. Also the Elite that had his stomach scramblified, that also tells us that the Flood was released before the marines arrived. What ponders me is the wacko marine that shoots you. We all thought that all marines in the captainힿs squad had died, but this tells us otherwise. He must have survived because of 2 reasons:

1: he knows the Floodힿs image

2: he has wet his pants (either literally or an expression) in fear, telling me he has witnessed the events that occurred.

This scene is also on my mind. Some people playing Halo try to get out the way they came but find the elevator burnt and destroyed. 3 different reasons and anyone can be true:

1: the Flood that already broke loose might have secured the area above when you were meeting the Flood and destroyed the elevator either by blowing it up so that survivors will get stuck in the facility or they messed around and accidentally blew up the elevator.

2: the Flood that you meet in the chamber spread around the station destroy the elevator from below.

3: the Covenant might have ordered reinforcements and destroyed the lift blocking the floods way out sacrificing their own troops.

Another scene I guess people have already figured out. Deep in the station you enter a room from above where you watch 2 marines being violently beat up by flood. They are part of the rescue team at the end of the mission. So are the men that are killed with all the shotguns in the hallway and in the room after with dead jackals.

A list of possible flood mutations (most you probably know):

Elite = Elite Warrior

Grunt = Carrier Flood

Jackal = Carrier Flood

Human = Human Warrior

Hunter = None

Brute = Unknown because never seen but imagine an image of it. Now thatힿs scary!

Drone = Unknown but come on! Imagine a flying flood that would dive and whip you hard!

Prophet = I know this is weird but nobody has ever realised that Gravemind could be an infected prophet! Probably a prophet that the forerunners worshipped or something, evolved into a godly flood form because of years of containment and being around flood. Also you can view the first stages of an infected prophet in the beginning movie of the Gravemind level, guess who? Itힿs the paranoid prophet Regret!

Engineer = Possibly, quite possibly an I.Q form, what Keyes was turned into on Halo 1, level Keyes. If the engineer is infected and a high I.Q source is merged with it, it will form an I.Q form (or a blob of gooey flood) that is like infection forms only that it infects computer networks and absorbs data.